1. Field of the Invention
The present invention relates to exposure control systems for photographic apparatus, in general, and to such systems employing separate photodetectors for sensing visible and non-visible electromagnetic frequencies for controlling the amount of image-carrying scene light admitted to the film plane of such apparatus, in particular.
2. Description of the Prior Art
Automatic light responsive exposure control systems are well known in the photographic arts and have been long used to control the duration of a photographic exposure. In addition, photographic apparatus incorporating an electronic flash, such as that described in U.S. Pat. No. 4,444,478 to Kieth et al, in common assignment herewith, having an exposure control system that employs separate ambient and artificial light sensors whose outputs are integrated by separate integrators for exposure interval and electronic flash light-output control purposes, respectively, are also well known in the photographic art.
For a number of reasons (e.g. cost, size, power consumption, etc.) the electrical circuitry employed in the above-noted exposure control systems are often formed in an integrated circuit (IC). An IC, in its most general state, is an interconnected array of active and passive elements integrated with or deposited on a single semiconductor substrate and capable of performing one or more electronic circuit functions. An integrator such as that mentioned above for integrating the light levels sensed by a photodetector requires a considerable amount of valuable space in an IC when formed as a portion thereof. The implementation of a function within an IC requiring an electronic circuit or circuits needing a relatively large amount of space, such as the just-mentioned photodetector integrator, may prevent the inclusion of additional functions within the same IC because of a lack of available space.
In one type of electronic flash camera such as that sold by Polaroid Corporation of Cambridge, MA under its Registered Trademark Impulse Autofocus, two photodetectors whose outputs are coupled to separate integrators are employed to measure visible and infrared (IR) scene light content during an exposure interval. The camera includes a quench strobe and a scanning blade shutter. The electronic flash illuminates the scene with artificial light a subject distance related time after the scanning shutter opens. The infrared photodetector measures the IR content of the electronic flash light reflected from the scene and the visible light photodetector measures the ambient scene light during an exposure interval.
Heretofore the use of a single integrator to integrate the amount of scene light sensed by two different light sensors was avoided because switching the integrator between light sensors would introduce ringing and/or noise into the integrator of a magnitude that would produce substantial scene light level integration errors. In the exposure control system employed in the above-noted Polaroid camera there is no need to switch one integrator between two photodetectors because, as noted, each photodetector output is integrated by a separate integrator. However, the IC in this particular camera has less space available to accommodate additional functions because of the presence in the IC of these two integrators.